Correct way for creating houses with interior


I’m trying to make a house with interior, but stumbled on lighting artifacts and incorrect behavior. Mostly, the way I do building is by duplicating square plane with tiling texture and connecting to form a house shape. Then I push it in for interior. I do put the roof on top then in the similar way. But I do not weld some of the parts and just leave them as one face polygons intersecting each other. I belive Unreal doesn’t like that. I was wondering if I should rather use walls that actually have thickness?